Thin film resonator and method for manufacturing the same

ABSTRACT

A thin film resonator having enhanced performance and a manufacturing method thereof are disclosed. The thin film resonator includes a supporting means, a first electrode, a dielectric layer and a second electrode. The supporting means has several posts and a supporting layer formed on the posts. The first electrode, the dielectric layer and the second electrode are successively formed on the supporting layer. The thin film resonator is exceptionally small and can be highly integrated, and the thickness of the dielectric layer of the resonator can be adjusted to achieve the integration of multiple bands including radio, intermediate and low frequencies. Also, the thin film resonator can minimize interference and has ideal dimensions because of its compact substrate, making the thin film resonator exceptionally small, yet comprising a three-dimensional, floating construction.

This application is a division of 10/169,500 filed Jul. 3, 2002 now U.S.Pat. No. 6,762,471 which is a 371 of PCT/KR01/01894 filed Nov. 7, 2001.

TECHNICAL FIELD

The present invention relates to a thin film resonator and a method formanufacturing the same, and more particularly to an integrated thin filmresonator with multiple bands to enhance performance and an easy methodfor manufacturing the same.

BACKGROUND ART

Mobile communications has been rapidly developed as the main instrumentserving the information society. This instrument has been influenced bythe developments of two technologies: signal processing using modulationor demodulation of transmitted data over limited frequency bands, andthe technology of manufacturing radio frequency (RF) hardware parts.

In particular, filters are most important among the parts used for RFmobile communication devices. Filters are able to select the signalrequested by the user from numerous signals on the public communicationnetwork, or filter a signal transferred by the user. Thus, excellentfilters were previously developed for high quality mobile communication.Recently, higher performance filters have been developed to be thinnerand more light-weight. These features ensure that mobile communicationdevices consume less power and more portable.

In general, a resonator or a frequency filter is the device thattransmits the frequencies of a message in a predetermined band, andfilters the frequencies on other bands being produced by variouselectronic devices such as wireless phones, personal communicationservice devices, cellular phones or devices for the international mobiletelecommunications 2000 (IMT-2000) as a band pass filter.

Presently, the dielectric filter and the surface acoustic wave (SAW)filter are widely used as the RF filter for mobile communicationdevices. The dielectric filter has some advantages such as highpermeability, low insertion loss, stability at high temperatures andgood mechanical strength. However, the dielectric filter is too large tobe applied in a monolithic microwave integrated circuit (MMIC). Thoughthe mono-blocked or the multi-layered surface mounted device (SMD)resonators are now developed with smaller dimensions, SMD resonators donot sufficiently overcome their size problems.

SAW filters are relatively smaller than dielectric filters and havesimpler signal processing and more simplified circuits. The SAW filteralso can be manufactured using semiconductor technology, and gives highquality results since the SAW filter's side rejection in its pass-bandis greater than that of the dielectric filter. However, the SAW filterhas large insertion losses below 3 dB and its manufacturing costs arehigh because it is manufactured using single crystal piezoelectricsubstrate composed of lithium niobate (LiNbO₃) or lithium titanate(LiTaO₃). Also, the SAW filter is manufactured using an ultraviolet rayexposure apparatus so that the SAW filter may not be used for highfrequency bands above 5 GHz because the line width of the inter-digitaltransducer (IDT) is above 0.5 μm.

Film bulk acoustic resonators (FBAR) have been developed for nextgeneration mobile communication devices. The FBAR can be mass-producedat low cost using semiconductor technology and is ultra light weight andthin. In addition, the FBAR can be freely combined with RF activedevices. In particular, the FBAR has good insertion loss of about 1 to1.5 dB-smaller than or identical to that of the dielectric filter. TheFBAR also has excellent side rejection higher than the of the SAW filterby about 10 to 20 dB, thereby providing high quality results.

At present, the active elements of mobile communications include theHetero-junction Bipolar Transistor (HBT) or the Metal SemiconductorFiled Effect Transistor (MESFET), but these are gradually beingsimplified and minimized by monolithic microwave integrated circuit(MMIC) technology. However, passive components of RF technology such asthe filter, the duplexer filter or the antenna are relatively large andcomplicated structures so that the single chip may not be achieved dueto passive components.

The FBAR or the stacked thin film bulk wave acoustic resonators (SBAR)are manufactured by forming piezoelectric material such as zinc oxide(ZnO) or aluminum nitride (AIN) on a substrate composed of silicon orgallium-arsenic (Ga—As) using RF sputtering method, thereby achievingthe desired resonance provided by the piezoelectric material.

The thin film resonator can be manufactured at low cost and yet providehigh quality, making it is applicable for use in various devices withfrequency bands of 900 MHz to 10 GHz. In addition, the thin filmresonator can be much smaller than the dielectric filter and has theadded benefit of an insertion loss smaller than that of the SAW filter.Hence, a thin film filter such as FBAR can be used in any MMIC dependenton high quality and good stability.

The method for manufacturing conventional FBAR or the SBAR is disclosedat U.S. Pat. No. 6,060,818 issued to Richard C. Ruby et al.

FIG. 1 is a cross-sectional view showing the FBAR and FIGS. 2A to 2C arecross-sectional views illustrating the method for manufacturing the FBARin FIG. 1.

Referring to FIG. 1, the FBAR 10 is formed on a silicon substrate 15 andthe FBAR 10 includes a bottom electrode 20, a piezoelectric layer 25 anda top electrode 30.

An oxide layer 35 is formed on the substrate 15 and a pit 40 isinterposed between the substrate 15 and the FBAR 10.

Referring to FIG. 2A, the silicon substrate 15 is provided, and then thepit 40 having a predetermined depth is formed on the substrate 15 bypartially etching the substrate 15. Subsequently, the oxide layer 35 isformed on the whole surface of the substrate 15 by the thermal oxidationmethod.

As shown in FIG. 2B, after a sacrificial layer 45 composed of phosphorsilicate glass is coated on the oxide layer 35 to fill the pit 40, thesacrificial layer 45 is polished so that the sacrificial layer 40remains only in the pit 40.

Referring to, FIG. 2C, after the bottom electrode 20 composed ofmolybdenum (Mo), the piezoelectric layer 25 composed of aluminum nitride(AIN), and the top electrode 30 composed of molybdenum are successivelycoated on the oxide layer 35 and on the sacrificial layer 45 filling thepit 40, the bottom electrode 20, the piezoelectric layer 25, and the topelectrode 30 are patterned. Then, the sacrificial layer 45 is removedusing an etching solution containing hydrofluoric acid (HF), therebycompleting the FBAR 10 as shown in FIG. 1.

The conventional FBAR is, however, formed on the substrate where thecavity is positioned, giving the FBAR two-dimensional construction.Hence, the conventional FBAR provides poor quality performance with anincreased insertion loss.

In addition, the interference of the substrate may not be blocked,causing the power loss of the FBAR to increase. The size of the FBAR islimited also, since the FBAR is formed over the cavity in the substratein order to receive the deformation of the piezoelectric layer.

Furthermore, the process for etching the silicon substrate demands muchtime, and the cost of manufacturing the FBAR increases because theconventional FBAR is formed on the silicon substrate where the cavity ispositioned.

To overcome such problems, research institutes at Berkeley and MichiganUniversities have disclosed a thin film bulk acoustic resonator (TFBAR)with a three-dimensional structure on a substrate using themicro-electromechanical system (MEMS) technology. However, the TFBAR maynot be mass-produced and packaging the TFBAR may be difficult since itsstructure is complicated and the integration device including the TFBARis difficult.

DISCLOSURE OF THE INVENTION

The present invention is intended to overcome the disadvantagesdescribed above. Therefore, it is an object of the present invention toprovide a thin film resonator having an ultra minute size in order toachieve high integration with MEMS technology, and a method formanufacturing the thin film resonator.

It is another object of the present invention to provide a thin filmresonator manufactured to be a multiple frequency band integrated thinfilm resonator by controlling the thickness of piezoelectric layerthereof, and a method for manufacturing the thin film resonator.

It is still another object of the present invention to provide a thinfilm resonator having a three-dimensional, floating construction tominimize power loss due to interference from the substrate,corresponding in size to the size of the substrate, and a method formanufacturing the thin film resonator.

It is still another object of the present invention to provide a thinfilm resonator manufactured at low cost, yet giving high qualityresults, and a method for manufacturing the thin film resonator.

It is still another object of the present invention to provide a thinfilm resonator having minute patterns and a three-dimensional form inorder to obtain high quality results with low insertion loss, and amethod for manufacturing the thin film resonator.

To accomplish the objects of the present invention according to oneaspect of the present invention, there is provided a thin film resonatorfor filtering the frequency of a predetermined band comprising asupporting means having a plurality of posts formed on a substrate and asupporting layer formed on the posts, a first electrode formed on thesupporting means, a dielectric layer formed on the first electrode, anda second electrode formed on the dielectric layer.

There are four posts formed on the substrate so as to support thesupporting layer, and the supporting layer has a plurality of openingsformed adjacent to each post, respectively.

Preferably, the supporting layer, the first electrode, the dielectriclayer and the second electrode are each shaped like rectangular platesthat, in combination, create a pyramid shape.

The first and the second electrodes are composed of metals selected fromthe group consisting of platinum, tantalum, platinum-tantalum, gold,molybdenum and tungsten. The dielectric layer is composed of materialsselected from the group consisting of barium titanate, zinc oxide,aluminum nitride, lead zirconate titanate (PZT), lead lanthanumzirconate titanate (PLZT) and lead magnesium niobate (PMN).

The thin film resonator further comprises a connecting means forconnecting the second electrode to a circuit formed on the substrate.The connecting means has a central portion and lateral potions bent fromthe central portion so that the connecting means contacts the circuitand the second electrode. As a result, a first air gap is interposedbetween the substrate and the supporting means and a second air gap isinterposed between the second electrode and the connecting means. Inthis case, the connecting means is composed of metals selected from thegroup consisting of platinum, tantalum, platinum-tantalum, gold,molybdenum and tungsten.

To accomplish the objects of the present invention according to anotheraspect of the present invention, there is provided a method formanufacturing a thin film resonator for filtering frequencies on apredetermined band, which comprises the steps of forming a firstsacrificial layer on a substrate, partially etching the firstsacrificial layer to expose portions of the substrate, forming aplurality of posts on the exposed portions of the substrate, forming afirst layer on the posts and the first sacrificial layer, forming afirst metal layer on the first layer, forming a second layer on thefirst metal layer, forming a second metal layer on the second layer,forming a first electrode, a dielectric layer and a second electrode bypatterning the second metal layer, the second layer and the first metallayer, forming a supporting layer having a plurality of openings bypatterning the first layer, and removing the first sacrificial layerthrough the openings.

The first sacrificial layer is composed of poly silicon and formed by alow pressure chemical vapor deposition method and the first sacrificiallayer is partially etched by a photolithography method, a reactive ionetching method or an argon laser etching method.

The posts are created through forming a BPSG layer on the firstsacrificial layer and the substrate using a low pressure chemical vapordeposition method at temperatures under about 500° C., and polishing theBPSG layer to remove portions of the BPSG layer formed on the firstsacrificial layer. At that time, the BPSG layer is polished by achemical mechanical polishing method or an etch-back method.

The first layer is formed by a plasma enhanced chemical vapor depositionmethod or by using silicon oxide or phosphor oxide at temperatures fromapproximately 350 to 450° C.

The first and the second electrodes are formed by using metals selectedfrom the group consisting of platinum, tantalum, platinum-tantalum,gold, molybdenum and tungsten using a sputtering method or a chemicalvapor deposition method.

The second layer is formed from piezoelectric material orelectrostrictive material using a sol-gel method, a sputtering method, aspin coating method or a chemical vapor deposition method. The secondlayer is composed of materials selected from the group consisting ofbarium titanate, zinc oxide, aluminum nitride, lead zirconate titanate(PZT), lead lanthanum zirconate titanate (PLZT) and lead magnesiumniobate (PMN). In this case, the second layer is heat treated by a rapidthermal annealing method for the phase transition of the second layer.

The first sacrificial layer is removed with xenon fluoride or brominefluoride.

Preferably, the method for manufacturing the thin film resonatorcomprises the steps of forming a second sacrificial layer on thesubstrate and the second electrode, partially etching the secondsacrificial layer to expose a portion of the second electrode and acircuit formed on the substrate, forming a connecting means forconnecting the second electrode to the circuit, and removing the secondsacrificial layer.

The second sacrificial layer is composed of poly silicon or photo resistand formed by a low pressure chemical vapor deposition method or a spincoating method.

Preferably, the surface of the second sacrificial layer is planarizedusing a chemical mechanical polishing method or an etch-back method.

The connecting means is formed from metals selected from the groupconsisting of platinum, tantalum, platinum-tantalum, gold, molybdenumand tungsten using a sputtering method or a chemical vapor depositionmethod.

The second sacrificial layer is removed with xenon fluoride, brominefluoride, etching solution containing hydrofluoric acid, or by using anargon laser etching method. At that time, the steps for removing thefirst and the second sacrificial layers are simultaneously performed.

In general, the resonator for filtering frequencies on a band operatesaccording to the principle of resonance created due to a bulk acousticwave generated from the piezoelectric layer that lies between twoelectrodes. The process for manufacturing such a resonator generallyconsists of forming the piezoelectric film composed of zinc oxide (ZnO)or aluminum nitride (AIN) on a substrate composed of silicon orgallium-arsenic (Ga—As), and forming a membrane and electrodes.

In the resonator manufacturing process, the piezoelectric film is fixedto the electrode and the piezoelectric film is adequately thin and flat,and of adequately high density. According to the conventional method,after the P⁺ layer including a boron or silicon oxide layer, is formedon the silicon substrate by an ionic growth method, the bottom of thesilicon substrate is anisotropically etched until the membrane forms acavity formed in the substrate. Then, electrodes are formed on themembrane and the piezoelectric layer is interposed between theelectrodes by using an RF magnetron sputtering method to form the thinfilm resonator. The piezoelectric materials used to form thepiezoelectric layer requires a high specific resistance below 106 Ωcmwith a standard deviation below 60, a large electromechanical couplingconstant, and good cultivation. In addition, the piezoelectric materialshould have high breaking strength and quality reproduction results.However, the manufacturing process, including production of theabove-mentioned membrane products, experiences much failure because themembrane may be fractured when the thin film resonator is separated forpackaging. Also, the thin film resonator may have low resonancecharacteristics because acoustic wave energy is lost due to themembrane. Recently, an air gap typed FBAR or a brag reflector typed FBARhas been used to reduce this loss of acoustic wave energy due to themembrane, and to simplify the resonator manufacturing process.

As for the air gap type of FBAR, after a sacrificial layer is formed ona silicon substrate using micro-machining technology, the air gap isformed at the point where the sacrificial layer is located. Hence, themanufacturing time and the generation of harmful gases can be reducedwithout using back-etching to form the membrane.

In the brag reflector typed FBAR, materials, each with differentacoustic impedances, are alternatively formed on the silicon substrateto facilitate the brag reaction, thereby generating the resonance of theacoustic wave energies between electrodes. The brag reflector typed FBARcan be utilized as a ladder filter, a monolithic crystal filter, astacked filter or a lattice filter can be a one chip type of thin filmresonator. Such resonators may be manufactured quickly and have highmechanical strength, but their low electromechanical coupling constantis reduced by 30% when compared to the conventional FBAR.

According to the present invention, the thin film resonator ismanufactured using MEMS technology without etching the substrate to haveminute dimensions below hundreds of micrometers. Hence, the thin filmresonator is exceptionally small and can be highly integrated onto thesubstrate. Also, the thickness of the dielectric layer of the thin filmresonator can be adjusted to achieve the integration of multiple bandsincluding radio frequency (RF), intermediate frequency (IF) and lowfrequency (LF) by controlling the thickness of the dielectric layer.Also, an inductor and a capacitor can be integrated.

In addition, yields can be increased and manufacturing costs can begreatly reduced since the thin film resonator can be manufacturedwithout etching or machining the silicon substrate. Therefore, themanufacturing process of the present invention has excellent advantagesduring mass production, including simplicity and ease of packaging.Also, the thin film resonator of the present invention has a goodquality factor of about 1000 to 10000 and a low insertion loss of under2 dB, because the thin film resonator has minute patterns and athree-dimensional, floating construction, and is easily manufacturedusing the MEMS technology.

Furthermore, the thin film resonator of the present invention canminimize any interference due to its substrate, and has ideal dimensionsbecause of its compact substrate, making the thin film resonatorexceptionally small yet comprising three-dimensional, floatingconstruction.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and other advantages of the present invention willbecome more apparent through the detailed description of the preferredembodiments thereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view showing the conventional film bulkacoustic resonator;

FIGS. 2A to 2C are cross-sectional views illustrating a method formanufacturing the conventional film bulk acoustic resonator in FIG. 1;

FIG. 3 is a perspective view showing a thin film resonator according toone preferred embodiment of the present invention;

FIG. 4 is a cross-sectional view showing the thin film resonator in FIG.3; and

FIGS. 5A to 5I are cross-sectional views illustrating a method formanufacturing the thin film resonator in FIG. 4.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in more detail with reference to the accompanying drawings,but it is understood that the present invention should not be limited tothe following embodiments.

FIG. 3 is a perspective view showing a thin film resonator according toone preferred embodiment of the present invention and FIG. 4 is across-sectional view showing the thin film resonator in FIG. 3.

Referring to FIGS. 3 and 4, a thin film resonator 100 according to thepresent invention has a supporting member 190, a first electrode 165, adielectric layer 175 and a second electrode 185. The thin film resonator100 is formed on a substrate 110 and a first air gap 200 is interposedbetween the thin film resonator 100 and the substrate 110.

The supporting member 190 supports the thin film resonator 100 andincludes a supporting layer 155 and a plurality of posts 140 and 141.The supporting layer 155 is composed of silicon nitride (AIN) and theposts 140 and 141 are respectively composed of boro-phosphor silicateglass (BPSG).

In the present embodiment, four posts are formed at predeterminedportions of the substrate 110, respectively. The supporting layer 155has the shape of a rectangular plate supported by the posts 140 and 141.

In addition, a plurality of openings 195 and 196 are formed throughportions of the supporting layer 155 adjacent to the posts 140 and 141respectively, so that the supporting layer 155 including those openings195 and 196 performs a stress balancing role to prevent the thin layersof the thin film resonator 100 from bending while several thin layersare stacked to form the thin film resonator 100. The posts 140 and 141support the supporting layer 155 and the structure thereon, and thefirst air gap 200 is interposed between the substrate 110 and thesupporting layer 155. As a result, the thin film resonator 100 has athree-dimensional, floating construction, thereby minimizing power lossdue to interference from the substrate 110.

The first electrode 165, the dielectric layer 175 and the secondelectrode 185 are successively formed on the supporting member 190. Thefirst electrode 165, the dielectric layer 175 and the second electrode185 respectively have rectangular plate shapes.

The first and the second electrode 165 and 185 are composed of metalshaving good electrical conductivity such as platinum (Pt), tantalum(Ta), platinum-tantalum (Pt—Ta), gold (Au), molybdenum (Mo) or tungsten(W). The dielectric layer 175 is composed of piezoelectric materialssuch as barium titanate (BaTiO₃), zinc oxide (ZnO), aluminum nitride(AIN), lead zirconate titanate (PZT; Pb(Zr, Ti)O₃), lead lanthanumzirconate titanate (PLZT; (Pb, La)(Zr, Ti)O₃). Also, the dielectriclayer 175 is composed of electrostrictive materials, for example leadmagnesium niobate (PMN; (Pb(Mg, Nb)O₃). Preferably, the dielectric layer175 is composed of PZT.

The first electrode 165 is smaller than the supporting layer 155, andthe dielectric layer 175 is smaller than the first electrode 165. Also,the second electrode 185 is smaller than the dielectric layer 175, sothat the thin film resonator 100 generally has the shape of a pyramid.

A connecting member 220 is formed from a circuit 205 to the secondelectrode 185 so as to connect the thin film resonator 100 with thecircuit 205 formed on the substrate 110. The connecting member 220 has ashape of a bridge to connect the thin film resonator 100 with the secondelectrode 185, so that the thin film resonator 100 has athree-dimensional, floating construction. Both end portions of theconnecting member 220 are bent to contact with the second electrode 185and the circuit 205 respectively. The central portion of the connectingmember 220 has the shape of a reverse ‘U’. That is, the lateral portionsof the connecting member 220 are primarily bent from the central portionof the connecting member 220 in a downward direction, and then thelateral portions of the connecting member 220 are secondarily bent inhorizontal directions, respectively. Hence, the end portions of theconnecting member 220 are attached to the second electrode 185 and thecircuit 205 respectively. The connecting member 220 is composed ofmetals having good electrical conductivity such as platinum, tantalum,platinum-tantalum, gold, molybdenum or tungsten.

Hereinafter, the method for manufacturing the thin film resonatoraccording to one preferred embodiment of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIGS. 5A to 5I are cross-sectional views illustrating the method formanufacturing the thin film resonator in FIG. 4. In FIGS. 5A to 5I, thevarious elements have the same reference numerals as in FIGS. 3 and 4.

Referring to FIG. 5A, a first sacrificial layer 120 having the thicknessof about 1 to 3μ, is formed on the substrate 100 by a low pressurechemical vapor deposition (LPCVD) method. The first sacrificial layer120 is composed of poly silicon. In this case, the substrate 110 iscomposed of silicon or an insulating material such as glass or ceramic.

Subsequently, the first sacrificial layer 120 is partially etched usinga photolithography method or a reactive ion etching method, therebyforming holes 130 and 131 that expose portions of the substrate 110. Atthat time, four holes are formed with reference to FIG. 3 though onlytwo holes 130 and 131 are shown in FIG. 5A.

Referring to FIG. 5B, a BPSG film 135 is formed on the first sacrificiallayer 120 and in the holes 130 and 131. The BPSG layer 135 is formed attemperatures below 500° C. using an LPCVD method. The BPSG layer 135 hasa thickness of approximately 2.0 to 3.0 μm and the holes 130 and 131that expose the substrate 110 are filled with the BPSG layer 135.

Referring to FIG. 5C, the BPSG layer 135 is polished using a chemicalmechanical polishing method or an etch-back process to partially removethe portion of the BPSG layer 135 formed on the first sacrificial layer120. Thus, portions of the BPSG layer 135 only remains in the holes 130and 131 formed through the first sacrificial layer 120. The remainingportions of the BPSG layer 135 become the posts 140 and 141 forsupporting the thin film resonator 100. The posts 140 and 141 and thesuccessive supporting layer 155 together form a supporting member forsupporting the thin film resonator 100. In this case, four postscomposed of BPSG are formed as shown in FIG. 3 and the shapes of theposts are determined by the shapes of the holes formed through the firstsacrificial layer 120. Hence, the posts assume the shapes of squarepillars when the holes have rectangular cross sections, but assume theposts have the shapes of tubular columns when the holes have circularcross-sections. Also, when the holes have triangular cross sections, theposts assume the shape of triangular pillars.

Four posts are formed to enhance the stability of the thin filmresonator 100, however, the number of the posts can be increased orreduced in accordance with the consumer's requirements for structuralstability in the thin film resonator 100 according to another embodimentof the present invention.

In another embodiment of the present invention, the upper portion of thefirst sacrificial layer 120 can be partially polished while the BPSGlayer 135 is being polished. Therefore, the surface of the firstsacrificial layer 120 becomes more even, thereby enhancing theconsistent flatness of the thin film resonator 100. According to stillanother embodiment of the present invention, the thin film resonator 100can still have an enhanced flatness, even though the upper portion ofthe first sacrificial layer 120 is polished separately after the firstsacrificial layer 120 is coated on the substrate 110.

Referring to FIG. 5D, a first layer 150 composed of silicon nitride(Si_(x)N_(y)) is formed on the first sacrificial layer 120 and the posts140 and 141. The first layer 150 has a thickness of approximately 0.1 to1.0 μm resulting from treatment using a plasma enhanced chemical vapordeposition (PECVD) method. The first layer 150 will be patterned to formthe supporting layer 155. According to another embodiment of the presentinvention, the first layer 150 can be composed of low temperature oxide(LTO) such as silicon oxide (SiO_(x)) or phosphor oxide (P₂O₅) attemperatures ranging from approximately 350 to 450° C.

Then, a first metal layer 160 is formed on the first layer 150. Thefirst metal layer 160 is composed of metals having excellent electricalconductivity and good adhesive strength such as platinum, tantalum,platinum-tantalum, gold, molybdenum or tungsten. The first metal layer160 is formed using a sputtering method or a CVD method to have athickness of about 0.1 to 1.0 μm. The first metal layer 160 will bepatterned to form the first electrode 165.

A second layer 170 is formed on the first metal layer 160. The secondlayer 170 is composed of dielectric components such as piezoelectricmaterial or electrostrictive material. The second layer 170 is formed bya sol-gel method, a spin coating method, a sputtering method or a CVDmethod to achieve a thickness of about 0.1 to 1.0 μm. The second layer170 will be patterned to form the dielectric layer 175. The second layer170 is formed using barium titanate, zinc oxide, aluminum nitride, leadzirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT) orlead magnesium niobate (PMN). Preferably, the second layer 170 is formedby spin coating the PZT, and is manufactured by a sol-gel method to havea thickness of about 0.4 μm.

According to another embodiment of the present invention, the secondlayer 170 is heat-treated using a rapid thermal annealing (RTA) methodto drive the phase transition of the piezoelectric material or theelectrostrictive material of the second layer 170 after the second layer170 is formed. Hence, the dielectric layer 175 can easily respond to anyelectric field generated between the first electrode 165 and the secondelectrode 185. Also, the mechanical responsiveness of the dielectriclayer 175 can easily transfer energy to the first and the secondelectrodes 165 and 185. That is, the dielectric layer 175 convertselectrical energy to sound wave energy when an electric field isgenerated between the first electrode 165 and the second electrode 185,and voltage is applied to the thin film resonator 100. The sound waveproceeds in the same direction as the electric field, and reflects fromthe interface between the second electrode 185 and the air, therebyoperating the thin film resonator 100 as a filter.

Then, a second metal layer 180 is formed on the second layer 170. Thesecond metal layer 180 is composed of a metal identical to the firstmetal layer 160 which could be platinum, tantalum, platinum-tantalum,gold, molybdenum or tungsten. The second metal layer 180 is formed bymeans of a sputtering method or a CVD method so that the second metallayer 180 has a thickness of about 0.1 to 1.0 μm. The second metal layer180 will be patterned to form the second electrode 185.

Referring to FIG. 5E, after a photo resist (not shown) is coated on thesecond metal layer 180 and the photo resist is patterned to form a photoresist pattern, the second metal layer 180 is patterned to have theshape of a rectangular plate by using the photo resist pattern as anetching mask, thereby forming the second electrode 185 (see FIG. 3).

Then, the second layer 179 and the first metal layer 160 aresuccessively patterned using the above-described method after the protoresist pattern is removed. Thus, the dielectric layer 175 and the firstelectrode 165 respectively have the shapes of rectangular plates, andare formed as shown in FIG. 3. In this case, the dielectric layer 175 islarger than the second electrode 185 and the first electrode 165 islarger than the dielectric layer 175. Therefore, the first electrode165, the dielectric layer 175 and the second electrode 185 combine toform the shape of a pyramid.

Referring to FIG. 5F, the first layer 150 is patterned using a reactiveion etching method or a photolithography method so as to form thesupporting layer 155 including the openings 195 and 196 that areadjacent to the posts 140 and 141 respectively. At that time, theopenings 195 and 196 are preferably formed during the patterning of thefirst layer 150 that forms the supporting layer 155. However, theopenings 195 and 196 are formed after the supporting layer 155.

The openings 195 and 196 perform as passages for injecting the etchingsolution or ions used to etch the first sacrificial layer 120, therebyeasily removing the first sacrificial layer 120. This minimizesinterference from the thin film resonator 100 due to the substrate 110,because four openings are formed as shown in FIG. 3.

Referring to FIG. 5G, the first sacrificial layer 120 is removed byusing an etching solution that includes hydrofluoric (HF) acid throughthe openings 195 and 196, and then the thin film resonator 100 is formedafter a washing and a drying processes are performed. The firstsacrificial layer 120 can also be removed by using xenon fluoride (XeF₂)or bromine fluoride (BrF₂). Furthermore, the first sacrificial layer 120can be removed by means of an argon laser etching method. The first airgap 200 is formed at the point of the first sacrificial layer 120 as thefirst sacrificial layer 120 is removed. That is, the thin film resonator100 is formed on the substrate 110 and the first air gap 200 isinterposed between the substrate 110 and the thin film resonator 100.

Referring to FIG. 5H, a second sacrificial layer 210 is coated on thewhole surface of the substrate 110 where the thin film resonator 100 isformed as above described after the circuit 205 is created on thesubstrate 110. The second sacrificial layer 210 is composed of polysilicon using an LPCVD method identical to that used to form the firstsacrificial layer 120. In addition, the second sacrificial layer 210 canbe composed of photo resist added using a spin coating method. In thiscase, the surface of the second sacrificial layer 210 can be polished bya chemical mechanical polishing method in order to enhance the flatnessof the second sacrificial layer 210. Also, the surface of the secondsacrificial layer 210 can be planed using an etch-back process.

Subsequently, the second sacrificial layer 210 is partially etched usinga photolithography process or an argon laser etching process topartially expose the second electrode 185 of the thin film resonator 100and the circuit 205 formed on the substrate 110.

Referring to FIG. 5I, a third metal layer is formed on the exposedportion of the second electrode 185, the exposed portion of the circuit205 and the second sacrificial layer 210. The third metal layer iscomposed of a metal identical to that of the first metal layer 160 suchas platinum, tantalum, platinum-tantalum, gold, molybdenum or tungsten.The third metal layer is deposited by a sputtering method or a CVDmethod so that the third metal layer has a thickness of about 0.1 to 1.0μm.

Then, the third metal layer is patterned to form the connecting member220 that electrically connects the thin film resonator 100 to thecircuit 205 on the substrate 110.

Subsequently, the second sacrificial layer 210 is removed by an etchingsolution containing hydrofluoric acid, xenon fluoride, bromine fluorideor by suing an argon laser etching method. Then, the thin film resonator100, having the connecting member 220 is completed after a washing and adrying process are performed. When the second sacrificial layer 210 isremoved, a second air gap 225 is formed at the point where the secondsacrificial layer 210 was positioned, so that the second air gap 225 isinterposed between the substrate 110, the thin film resonator 100 andthe connecting member 220.

In one preferred embodiment of the present invention, after the firstsacrificial layer 120 is removed, the connecting member 220 is formed onthe second sacrificial layer 210, and then the second sacrificial layer210 is removed. However, according to another embodiment of the presentinvention, the first and the second sacrificial layers 120 and 210 aresimultaneously removed after the connecting member 220 is formed on thesecond sacrificial layer 210 without removing the first sacrificiallayer 120. By using this production method, the manufacturing time andcosts can be reduced.

While this invention has been described and shown as having multipledesigns, the present invention may be further modified within the spiritand scope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

INDUSTRIAL APPLICABILITY

As it is described above, the thin film resonator of the presentinvention is manufactured using the MEMS technology without etching thesubstrate to have minute dimensions under hundreds of micro meters.Hence, the thin film resonator is exceptionally small and can be highlyintegrated onto the substrate.

Also, the thickness of the dielectric layer of the thin film resonatorcan be adjusted to achieve the integration of the multiple bandsincluding radio frequency (RF), intermediate frequency (IF) and lowfrequency (LF) by controlling the thickness of the dielectric layer.Also, an inductor and a capacitor can be integrated.

In addition, the yield can be increased and the manufacturing costsgreatly reduced since the thin film resonator can be manufacturedwithout etching or machining the silicon substrate. Therefore, themanufacturing process of the present invention has excellent advantagesduring mass production, including simplicity and ease of packaging.

Also, the thin film resonator of the present invention has a goodquality factor of about 1000 to 10000 and a low insertion loss of under2 dB because the thin film resonator has minute patterns and athree-dimensional, floating construction that is easily manufactured bythe MEMS technology.

Furthermore, the thin film resonator of the present invention canminimize interference from the substrate and has ideal dimensionsbecause of its compact substrate, making the thin film resonatorexceptionally small. Yet having a three-dimensional, floatingconstruction.

1. A method for manufacturing a thin film resonator for filteringfrequencies of a predetermined band, which comprises the steps of:forming a first sacrificial layer on a substrate; partially etching saidfirst sacrificial layer to expose portions of said substrate; forming aplurality of posts on the exposed portions of said substrate; forming afirst layer on said posts and said first sacrificial layer; forming afirst metal layer on said first layer; forming a second layer on saidfirst metal layer; forming a second metal layer on said second layer;forming a first electrode, a dielectric layer and a second electrode bypatterning said second metal layer, said second layer and said firstmetal layer; forming a supporting layer having a plurality of openingsby patterning said first layer; and removing said first sacrificiallayer through said openings.
 2. The method for manufacturing a thin filmresonator as recited in claim 1, wherein said first sacrificial layer iscomposed of poly silicon and formed by a low pressure chemical vapordeposition method.
 3. The method for manufacturing a thin film resonatoras recited in claim 1, wherein said first sacrificial layer is partiallyetched by a photolithography method, a reactive ion etching method or anargon laser etching method.
 4. The method for manufacturing a thin filmresonator as recited in claim 1, wherein the step for forming said postsfurther comprises: forming a BPSG layer on said first sacrificial layerand said substrate; and polishing said BPSG layer to remove portions ofsaid BPSG layer formed on said first sacrificial layer.
 5. The methodfor manufacturing a thin film resonator as recited in claim 4, whereinsaid BPSG layer is formed by a low pressure chemical vapor depositionlayer at temperatures under approximately 500° C.
 6. The method formanufacturing a thin film resonator as recited in claim 4, wherein saidBPSG layer is polished by a chemical mechanical polishing method oretch-back method.
 7. The method for manufacturing a thin film resonatoras recited in claim 1, wherein said first layer is formed by a plasmaenhanced chemical vapor deposition method.
 8. The method formanufacturing a thin film resonator as recited in claim 1, wherein saidfirst layer is formed by using silicon oxide or phosphor oxide attemperatures of about 350 to about 450° C.
 9. The method formanufacturing a thin film resonator as recited in claim 1, wherein saidfirst and said second electrodes are formed from metals selected fromthe group consisting of platinum, tantalum, platinum-tantalum, gold,molybdenum and tungsten and by using a sputtering method or a chemicalvapor deposition method.
 10. The method for manufacturing a thin filmresonator as recited in claim 1, wherein said second layer is formedfrom piezoelectric material or electrostrictive material and by using asol-gel method, a spin coating method, sputtering method or a chemicalvapor deposition method.
 11. The method for manufacturing a thin filmresonator as recited in claim 10, wherein said second layer is composedof material selected from the group consisting of barium titanate, zincoxide, aluminum nitride, lead zirconate titanate (PZT), lead lanthanumzirconate titanate (PLZT) and lead magnesium niobate (PMN).
 12. Themethod for manufacturing a thin film resonator as recited in claim 1,wherein the step for forming said second layer further comprises heattreating said second layer by using a rapid thermal annealing method forphase transition of said second layer.
 13. The method for manufacturinga thin film resonator as recited in claim 1, wherein said firstsacrificial layer is removed using xenon fluoride or bromine fluoride.14. The method for manufacturing a thin film resonator as recited inclaim 1, further comprising the steps of: forming a second sacrificiallayer on said substrate and said second electrode; partially etchingsaid second sacrificial layer to expose a portion of said secondelectrode and a circuit formed on said substrate; forming a connectingmeans for connecting said second electrode to said circuit; and removingsaid second sacrificial layer.
 15. The method for manufacturing a thinfilm resonator as recited in claim 14, wherein said second sacrificiallayer is composed of poly silicon or photo resist and formed by using alow pressure chemical vapor deposition method or a spin coating method.16. The method for manufacturing a thin film resonator as recited inclaim 14, further comprising the step of planarizing the surface of saidsecond sacrificial layer by using a chemical mechanical polishing methodor an etch-back method.
 17. The method for manufacturing a thin filmresonator as recited in claim 14, wherein said connecting means isformed by using metals selected from the group consisting of platinum,tantalum, platinum-tantalum, gold, molybdenum and tungsten and by usinga sputtering method or a chemical vapor deposition method.
 18. Themethod for manufacturing a thin film resonator as recited in claim 14,wherein said second sacrificial layer is removed by using xenonfluoride, bromine fluoride, or an etching solution includinghydrofluoric acid or by using an argon laser etching method.
 19. Themethod for manufacturing a thin film resonator as recited in claim 14,wherein the steps for removing said first and said second sacrificiallayers are simultaneously performed.